Wheat price improvements warrant conscientious pest management

With wheat prices as high as most Southwest farmers have ever seen them, protecting the crop from insect pests will be job one for most growers this winter. “The changing economics emphasizes the importance of insect pests causing economic damage,” says Chris Sansone, Texas AgriLife Extension Service entomologist.

Sansone discussed pest management strategies for small grains during the recent Ag Technology Conference on the Texas A&M-Commerce campus. He recommended an IPM approach to managing pests. He said any pest management should be compatible with other production practices, take advantage of multiple methods of pest suppression and be economically and environmentally sound.

Seed treatments are playing an increasingly important role in IPM for wheat, he said. “The high price of wheat has made this tool a viable option for producers. Currently, growers have Gaucho and Cruiser seed treatments. Benefits include elimination of spray drift, localized in the area of need and may have an immediate effect on pest populations. “We can eliminate the problem before symptoms occur,” Sansone said.

Precautions include potential for phytotoxicity. Also, seed coverage is crucial. Seed treatment is an early-season strategy and is preemptive, which may not be necessary every year.

He said grasshoppers have become a problem on early planted wheat in the past few years. “We have more than 150 species (of grasshoppers) in Texas,” he said. “As few as 30 per yard will eat one ton of vegetation in 10 days. They eat half their weight each day.”

He said grasshopper invasions involve more than one species and destroy vegetation indiscriminately. Outbreaks often follow drought.

Grasshoppers (except for red-legged and migratory species) produce only one generation per year but that's plenty, Sansone says. A female lays 200 eggs, as few as 40 in a bad year but as many as 400 in a good one.

“Hatch starts in April but females may not lay all their eggs at the same time. Also, different species hatch at different times.”

Producers should base treatment decisions on scouting the field margins as well as in the field. A count of 15 to 28 grasshoppers per square yard in the field is considered severe. More than a 28 count in the field is considered very severe. A count of 80 in field margins is very severe.

In a test conducted by Jim Swart and Allen Knutson, entomologists with AgriLife Extension, seed treatments accounted for as many as 12.3 dead grasshoppers per square foot in 2007 tests. That rate was with Gaucho, two ounces on 90 pounds of seed. Cruiser at two ounces on 90 pounds of seed resulted in 11.5 dead grasshoppers per square foot.

Cruiser at 1 1/3 ounces with 90 pounds of seed resulted in 9.5 dead grasshoppers. That dropped to 9.3 in 45 pounds of seed.

Greenbugs in wheat pose problems by threatening early stands. Sansone recommends checking for greenbugs in natural hosts such as Johnsongrass and dallisgrass prior to planting. “Also, look for natural enemies.”

Treatment thresholds depend on plant height and vigor. At 3 to 6 inches, 100 to 200 greenbugs per foot of row may cause economically harmful damage. At 6 to 8 inches, the number jumps to 200 to 400 and to 400 to 800 at 8 to 16 inches.

Management strategies should include weekly scouting, especially early in the season.

Current resistant options include TAM 107 (biotype C), TAM 110 (biotypes E, I and K) and TAM 112 (improved 110). “However, producers should plant varieties that are well adapted for the region.”

Sansone also recommends differentiating between wheat for grain and for grazing. For grazing he recommends Gaucho or Cruiser seed treatments. “Greenbug thresholds are not static and producers should consider a number of factors before treating. Recognize the growth stage, early versus late wheat and stressed and non-stressed wheat. Plant population is also a factor in infestation management.

“And don't underestimate the impact of grazing,” Sansone says.

Hessian fly does not infest wheat throughout the Southwest region, but where it shows up it can be devastating. Most infestations are confined to central and Northeast Texas.

Sansone says the fly oversummers as larva in puparium. Their emergence in the fall is based on temperature and rainfall. “Larval activity ceases in colder weather (below 40 degrees F). Adults emerge again from March through May.”

Symptoms of fall infestations include death of tillers, stunting and death of plants, thin stands, and reduced forage production. “Significant grain losses can be expected when more than 5 percent to 8 percent of stems are infested with Hessian fly in the fall,” he says.

Spring infestations may include stunting, death of tillers, reduced head size, and lodging. “Significant grain loss can be expected when more than 20 percent of the stems are infested by Hessian fly in the spring,” Sansone says.

Wheat is the preferred host, but the fly also infests rye, barley, and wild grasses such as Western wheatgrass, little barley and quackgrass.

Sansone says a complication to management is the number of Hessian fly biotypes that may infest wheat. “A biotype is an insect that looks the same but has different genetic characteristics, much like races of rust.”

Consequently, varieties resistant or tolerant to one biotype may be susceptible to others. “Don't put all your eggs in one basket,” Sansone says. “Reliance on one resistant variety will select for a different biotype in the area.”

He says 16 biotypes have been identified in Texas. Resistance is not a sure thing. “We know which genes are effective but for most wheat varieties we do not know what genes, if any, they carry for resistance to Hessian fly. Assessment of Hessian fly infestation in field trials is the best source of information on which varieties have resistance to the current local Hessian fly population.”

Late planting may beg a bit of explanation, Sansone says. “The main emergence usually takes place from late August to mid-October. Adults may continue to emerge until frost.”

He noted that Allen Knutson found low levels of Hessian fly puparium in seed from a heavily infested field so seed should be cleaned thoroughly before planting.

Sansone says natural enemies (parasites) have provided good control of the Hessian fly in the North Texas region. Parasites are not effective in the western part of the state due to dry conditions. The parasites are severely affected by drought. It may take a few years for parasites to build back up to adequate levels after a drought.

Plans for the 2007-2008 crop year include evaluating Gaucho and Cruiser and selected varieties for Hessian fly resistance.

“Gaucho and Cruiser have activity on Hessian Fly,” he says. “The main effect is reducing the first generation. Higher rates may last longer but we have questions about economic return.”